Question

Which of the following is FALSE concerning glycogen degradation?

A. Debranching enzyme transfers three glucose units to the non-reducing end of a nearby branch.
B. Glycogen phosphorylase cleaves fewer than four residues from a branch point.
C. Glycogen phosphorylase produces glucose-1-P.
D. Debranching enzyme cleaves α-1,6 bonds to release glucose.

Answer 1

The false statement about glycogen degradation is that the debranching enzyme cleaves α-1,6 bonds to release glucose; this enzyme actually transfers glucose units before cleaving the last α-1,6 bond to release a single glucose molecule.

Step-by-step explanation:

The incorrect statement concerning glycogen degradation is: D. Debranching enzyme cleaves α-1,6 bonds to release glucose. This statement is false because the debranching enzyme has two activities: it initially functions as a glucan transferase, moving a small oligoglucose unit from one branch to another, and secondly, it acts as an amylase to cleave the α-1,6 bond at the branch point, releasing a single glucose molecule, not glucose-1-phosphate as it would if it were cleaving α-1,4 glycosidic bonds.

Glycogen degradation, or glycogenolysis, involves glycogen phosphorylase which removes glucose units in the form of glucose-1-phosphate until it approaches a branch point, at which it stops working when four residues remain. The debranching enzyme then transfers three of the remaining glucose units to another chain and cleaves the remaining α-1,6 linkage to release free glucose.